1. Field of the Invention
The present invention relates to a solid electrolytic capacitor and a method for making a solid electrolytic capacitor.
2. Description of the Related Art
A typical solid electrolytic capacitor includes a porous sintered body that actions as an anode, and a dielectric layer, a solid electrolyte layer and a cathode layer which are formed on the porous sintered body. A technique for manufacturing a solid electrolyte layer is disclosed in e.g. JP-A-2008-311582. According to this technique, a solid electrolyte layer is provided by separately forming an inner electrode layer to be positioned inside the porous sintered body and an outer electrode layer to be positioned outside the porous sintered body. In this technique, after the dielectric layer and the inner electrode layer are formed, the outer electrode layer is formed by applying a dispersion material liquid, which contains a conductive polymer dispersion material and a solvent, to the porous sintered body and then removing the solvent. According to this technique, it is not necessary to infiltrate the dispersion material liquid into the small holes in the porous sintered body. This is advantageous in that, as the conductive polymer dispersion material, a material suitable for reducing the ESR (Equivalent Series Resistance) of a solid electrolytic capacitor can be selected without limitation.
However, the surface of the outer electrode layer formed by the above-described technique tends to be smooth, as compared with e.g. the surface of a solid electrolyte layer formed by chemical polymerization. Thus, cracking may occur between the solid electrolyte layer and the cathode layer. Further, since the outer electrode layer and the cathode layer are made of considerably different materials, a large contact resistance may be generated at the contact surfaces. This may leads to a high ESR of the solid electrolytic capacitor.